In liquid crystal displays, a linear polarization plate or a circular polarization plate is used for controlling the optical rotary strength or the double refraction property in the display. The circular polarization plate is also used in organic electroluminescence displays for preventing reflection of external light.
Hitherto, an anisotropic dye layer is widely used, which is obtained by dissolving or adsorbing iodine or a dichroic dye to a polymer material such as poly(vinyl alcohol) and stretching the obtained layer in a certain direction in a form of film to orient the dichroic dye; cf. Patent Document 1.
In usual anisotropic dye layer thus prepared, however, some problems are posed such as that the heat resistance or light resistance is insufficient or the yield rate of pasting the anisotropic dye layer in production course of the liquid crystal apparatus is low depending on the kind of dye or polymer material.
Therefore, a method is investigated, in which, the anisotropic dye layer is formed by that a coating liquid containing the anisotropic dye is coated on the substrate such as glass or transparent film by the wet layer forming method, and the dichroic dye is oriented by utilizing the interaction between the molecules of the dye; of. Patent Document 2, for example.
In the use as the polarization element, the anisotropic dye layer having high dichroic property is required for obtaining higher polarization ability. However, these usual anisotropic layers are inferior in the dichroic property. Therefore, the polarization element having superior polarization property cannot be obtained.
Hitherto, various dyes are used in the anisotropic dye layer and the selection of dye is one of important factors. For instance, it is described in Patent Document 1 that the dichroic dye represented by the following structural formula.

However, the compound described in Patent document 1 cannot be considered as sufficient for the material of the anisotropic dye layer formed by the wet layer forming method because the compound is insufficient in the dichroic property and low in the solubility in various solvents.
The anisotropic dye layer produced by the wet layer forming method is described in Patent Document 2, and the compound represented by the following structural formula are described as an example of usable dichroic dye.

However, the above compound causes a problem that the compound is easily decomposed since the compound is a dis-azo compound and a halogen atom is bonded with the triazine ring.
Moreover, patent Document 3 describes that the anisotropic dye layer having high anisotropy can be obtained by the use of a dichroic azo dye having a specific structure in which a triazinyl group and three or more azo bonds are included in the molecule thereof.
However, the dichroic ratio of the anisotropic dye layer obtained by such technology is insufficient even though the ratio is increased by the technology, and a technology capable of increasing the dichroic ratio is further demanded.
A layer having deep color is preferable for the polarization layer and the color is necessarily neutral. The neutral color is usually made by mixing two or more kinds of dichroic dye. However, large efforts have been required for coordinating the dichroic property of the dyes since the structures of the dyes are largely different from each other and the dichroic properties of them are also different.
As above mentioned, usually known dichroic dyes are insufficient in the performance thereof. Moreover, many problems are caused in the production process of the dye such as that many steps are required for synthesizing the objective substance from the raw materials and large effort is necessary for purifying the objective substance.
Besides, a coordination polymer having a repeating structure by the continuous interaction of metal ions and ligands has both of diversity of the metal ion as an inorganic compound and superior degree of freedom of the molecular design of the ligand as an organic compound. Consequently, it is expected that a spatial and electronic structure, which cannot realized by solely applying of an inorganic or organic compound, can be freely constructed for making possible to appear a new function; cf. Patent Document 4 for example. However, there is no example regarding that the coordination polymer functioning as the dichroic dye is applied to the anisotropic dye layer.
A polarizer having polarization properties has been used for a variety of uses for the purpose of display on the screen, light control, and the like. Further, elements, having functions such as display and light control, which utilize changes of the above polarization properties caused by external energy, have been known.
As the methods for changing the polarization properties of the polarizer, there has been known a method, for example, for changing orientation of liquid crystals by using thereof, or a method for changing orientation of dyes by using liquid crystals incorporating the dyes.
Further, methods for using chromic materials have been known. For example, there have been known a method, in which oriented photochromic dyes are used, and the dyes are colored by ultraviolet light irradiation and faded with visible light and the like to change their polarization properties (refer to Patent Document 5); and a method, in which a thermochromic material is used, which material is semitransparent or transparent under a prescribed temperature and develops color over a prescribed temperature (refer to Patent Document 6).
However, these methods, even though they have a function of polarization filter, are required to optionally carry out a change of the polarization properties, result in problems such as an insufficient. stability of polarization control against environmental fluctuations such as light and temperature, and an insufficient visual feature based on dependency of a viewing angle, in case where they are used, for example, display device in which constant polarization properties are required.
On the other hand, so-called electrochromic elements have been known as a light control element using chromic materials, and they have been utilized for display on the screen which carries out such as amount of light adjustment, and color adjustment by changing light absorption wavelength caused by supplying charges (refer to Patent Document 7).
These electrochromic elements only exhibit functions of light control or switching, and in case where a polarization function is required, a polarizer has to be separately prepared.
Moreover, as the embodiment in which variation of polarization property caused by externally applied energy is utilized, an embodiment is applicable in which a specified part of a polarization element is partially controlled for use. For example, an embodiment for giving the polarization ability to only a part of privacy film or that for displaying images on a displaying apparatus.
Even in such the case, some problems are posed in the usual method such as that the stability of the polarization control as to variation of environmental such as light and temperature is insufficient, the visual property based on the dependency on visual field angle and the constitution for simply and partially controlling is difficultly obtained.
An ellipse polarization plate is known as a functional plate using the polarization element.
The ellipse polarization plate has a retardation plate and a polarization plate and is used as an antireflection plate for reducing the external light reflection of the displaying apparatus using light emission elements.
As the ellipse polarization plate, a circular polarization filter constituted by laminating the polarization element containing the foregoing photochromic dye laminated with the retardation plate, cf. Patent Document 6, and a circular polarization film composed of a film having a specific retardation ability and polarization layer containing a dichroic liquid crystal dye, cf. Patent Document 8, have been known.
However, these elements require changing of the polarization property even though they have the polarization filter function. Therefore, problems such as that the stability of the visibility as to the variation of environmental condition such as light and temperature and the visibility based on the visible field angle dependency are insufficient are posed when the elements are used for an apparatus such as a displaying apparatus requiring stable polarization property.
Moreover, a treatment such as to remove the circular polarization film is necessary when the displaying apparatus or lighting apparatus is used for another purpose such as a mirror.
Patent Document 1: Japanese Patent application Publication No. H3-12606
Patent Document 2: International Publication No. 2002/099480 pamphlet
Patent Document 3: International Publication No. 2005/035667 pamphlet
Patent Document 4: Japanese Patent application Publication No. 2007-112769
Patent Document 5: Japanese Patent application Publication No. 2008-122485
Patent Document 6: Japanese Patent Application Publication No. 2005-538878
Patent Document 7: Japanese Patent Application Publication No. 2007-112957
Patent Document 8: Japanese Patent Publication Application No. 2007-025465